This Core will provide the critical subject retention, data collection, data management, and data analysis operations needed by the projects. The central functions of this core are to: -> maintain contact with the families and children participating in the clinical research center -> schedule data collection visits with children, parents, teachers and others providing data. -> administer the research protocols according to appropriate standards and in accord with the schedule for data collection. -> enter, store, and analyze the data obtained in conjunction with the investigators. A team of three field examiners, each living in the three communities in which the participants reside, will be trained and supervised in the conduct of the research protocols. These examiners will travel to the homes and/or schools of the participating children in order to obtain subject consent and to collect data as dictated by the needs of the three projects. These data will be routinely transferred back to the central laboratory where they will be entered in a computer database and securely stored. The data will then be disseminated to the appropriate investigators or data analysis will be performed by the Core statistical staff.